1. Technical Field
The disclosure relates in general to a semiconductor structure and a method for forming the same, and more particularly to a transistor and a method for forming the same.
2. Description of the Related Art
In recent years, green power technique has attracted attention. It is developed with a trend towards high conversion efficiency and low standby power consumption. A HV process has been widely used for a power supply such as a switch mode power supply. A switch mode power IC is formed by integrating a start-up circuit and a PWM circuit. A conventional start-up circuit for a HV device uses a resistor for providing a charging current to a charging capacitor until a voltage on the capacitor is achieved to a starting voltage of the PWM circuit. Then, the start-up circuit stops working. However, after stopping working, the resistor of the start-up circuit still dissipate powers. Therefore, power saving effect of the device is not good. In some techniques, the start-up circuit uses a transistor replacing the resistor. However, limited by electrical characteristics of the transistor, the transistor would have a high leakage current (higher than 100 μA) as the start-up circuit is in a stopping condition and a threshold voltage higher than 4V.